1. Field of the Invention
The present invention relates to power hand tools and more particularly, to a power hand tool having a torque control mechanism and an impact mechanism.
2. Description of the Related Art
A conventional power impact wrench is known comprising a motor, a transmission gear set, and an impact mechanism. The transmission gear set reduces the revolving speed of the rotary driving force of the motor to a predetermined level for output. The impact mechanism is adapted to produce an impact against the output shaft of the power hand tool intermittently and rapidly in same direction of rotation when the output shaft of the power hand tool encountered a resisting force that surpasses the output torque, for enabling the output shaft to overcome the resisting force and to keep working.
There is known an electric screwdriver, which comprises a motor, a transmission gear set, and a torque control mechanism. The transmission gear set reduces the revolving speed of the rotary driving force of the motor to a predetermined level for output. The torque control mechanism is adapted to set the maximum output torque of the electric screwdriver, preventing damage to the workpiece.
The aforesaid impact mechanism and torque control mechanism are designed to fit two reversed requirements. Normally, these two mechanisms do not coexist in a power hand tool. However, these two mechanisms may be required in a certain condition. For example, when a user uses an electric wrench to dismount a tire from a vehicle, the electric wrench needs an impact function to overcome the dismounting obstacle, which may be produced due to rust on the screw bolts at the tire or other reasons; in order to prevent damage to the screw bolts at the tire due to an excessive high torque when mounting the tire, it is necessary to have a torque setting function in the power hand tool. However, when arranging these two mechanisms in a power hand tool, the functioning of the torque setting mechanism may be damaged when starting the impact mechanism, and the impact mechanism fail to function when started the torque setting mechanism.
Therefore, it is desirable to provide a power hand tool having a torque control mechanism and an impact mechanism, which eliminates the aforesaid problem.